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ISCOIn-situ chemical oxidation
SK
B C
ahie
r IS
CO
In-situ
che
mical o
xidatio
n
SKB
The Centre for Soil Quality Management and Knowledge Transfer
(SKB) develops and transfers the knowledge needed by owners and
managers of plots of land and sites in order to effi ciently coordinate
the quality of the soil with the intended purpose. SKB supports the
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approaches and techniques in order to improve the coordination
between soil use and soil quality, and it improves wide social
acceptance thereof.
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On the basis of dedicated practical examples, the readers can apply
the subject to their own discipline.
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Cah
ier
1) Applies to both the classic Fenton’s reagent and the modified Fenton’s reagent application.2) Highly permeable soil is soil of a sandy composition containing little clay/loam, often homogeneous in structure, i.e. no or little
transitions of different compositions.3) Low permeable soil is soil built up of clay or loam, sometimes even peat, often heterogeneous in structure, i.e. many different soil
stratums of different compositions.
Overview tableOxidant Oxidation potential (mV) Level of experience Pollution situation Can be Cannot be applied to Time required for remediation & Favourable ambient Favourable ambient Unfavourable ambient Notes in the Netherlands applied to space required for minor factors for application factors for application factors for application to medium-sized pollution
Fenton’s reagent1)
Ozone/peroxide
Persulfate
Ozone
Permanganate
2.800
2.800
2.600 (activated)
2.600
1.700
highmore than 25 locationsmore than 3 contractors
medium5 - 25 locationsfewer than 3 contractors
lowfewer than 5 locationsfewer than 3 contractors
medium5 - 25 locationsfewer than 3 contractors
medium5 - 25 locationsmore than 3 contractors
source area - may or may not contain pure product, high groundwater levels
source area - may or may not contain pure product4), high groundwater levels in the plume area
source area - may or may not contain pure product, high groundwater levels
source area - may or may not contain pure product, high groundwater levels in plume area
source area - may or may not contain pure product, high groundwater levels
(chloro)ethenes, (chloro)ethanes, BTEX, light fraction mineral oil and PAH, free cyanides, phenols, phthalates, MTBE
(chloro)ethenes, (chloro)alkanes, mineral oil, BTEX, lighter fraction PAH, free cyanides, phenols, phtha-lates, MTBE
(chloro)ethenes, (chloro)alkanes, BTEX, lighter frac-tion PAH, phenols, phthalates, MTBE
(chloro)ethenes, mineral oil6), BTEX, lighter fraction PAH, free cyanides, phenols, phtha-lates, MTBE
chloroethenes, TEX8), phenols
weathered/heavy fraction mineral oil, higher alkanes, heavy fraction PAH, PCB, complex cyanides
heavy fraction PAH5), PCB5), complex cyanides
heavy fraction PAH, PCB
(chloro)alkanes, heavy fraction PAH, PCB, complex cyanides
benzene, (chloro)alkanes, mineral oil, PAH, PCB, cyanides
3 to 6 months, large - aboveground system, few to no other activities possible
source: 1 to 2 yearsplume: 2 to 5 yearslittle - underground system
0.5 to 1 year (based on experiences in the US) little - one-off injection of underground system
source: 1 to 2 yearsplume: 2 to 5 yearslittle - underground system
0.5 to 1 yearlittle - one-off injection of underground system
often less than 1 day
1 to 2 days
several weeks to months
1 to 2 days
several weeks
highly permeable soils2)
pH groundwater between 2 - 6 for classic Fenton’s
highly permeable soils
highly permeable soils
highly permeable soils in the unsaturated7) section of the soil, low humidity levels
highly permeable soils
low permeable soils3) soil that demands high levels of oxidant, a pH groundwater of 7.5 to 8 or higher and presence of calcium for classic Fenton’s, modified Fenton’s up to pH 10 applicable
low permeable soilspH of groundwater 8 to 9 or higher
low permeable soils high soil oxidant demand
low permeable soils, high soil oxidant demand, pH of ground-water 7.5 or higher
low permeable soils, high soil oxidant de-mand, in the event of an NOD of 2 g MnO
4·kg–1
soil, the application is no longer cost-effective
safety is important during implementation of technique, risk of mobilisation of heavy metals, add heavy metals with oxidant/ additives
safety important during implementation of techniqueozone generator on location
safety important during implementation of technique, persulfate must be activated
safety important during implementation of technique ozone generator on location
safety is important during implementation of technique, ground-water turns purple, add heavy metals with oxidant
4) According to the patent holder, not enough projects have been completed in the Netherlands to warrant application in soil that contains pure product.
5) According to the patent holder, breakdown does occur, but no practical examples from outside of the United States are known.6) Mineral oil is not fully broken down into water and carbon dioxide, but into smaller hydrocarbon chains7) The unsaturated section of the soil is that part that is located above the groundwater level.8) Permanganate cannot be applied in benzene contaminations, but it can be applied in the case of ethyl benzene, toluene and xylene(s).
Dealing with
soil
ISCO - In-situ chemical oxidation
ISCOIn-situ chemical oxidation
5
ISCO - In-situ chemical oxidation
In the Netherlands, in-situ chemical oxidation has been applied in soil remediation for a number of years now. This technique is abbreviated to ISCO. In the event of soil remedia-a-tion involving in-situ chemical oxidation, a strong oxidant is inserted in the soil. When the oxidant comes into contact with the pollution, it is broken down chemically (oxidized). This produces harmless compounds. Thanks to the relative simplicity of the technique and the fast degradation of the pollution, the technique is becoming increasingly popular as a means to treat the source of the pollution. Its popularity is further based on the large mass of pollution which can be removed from the soil in a short period of time. In addition, the so-called aftercare phase, the period in which the remain-der of the pollution must be monitored to establish the scope and the development thereof, is reached quicker and often involves lower levels of residual pollution compared to other in-situ techniques.
Five years ago, in-situ chemical oxidation was relatively new and still
in its experimental phase, with only a few specialist contractors
applying the technique in the Netherlands. Today, in 2006, multiple
contractors are active in the market offering a wide range of appli-
cations of in-situ chemical oxidation for the removal of small and
large-scale soil pollution. The technique has become fully-fledged
in the Netherlands and forms a standard part when considering the
remediation options. In spite of this, the technique is still largely
unknown among the public. The objective of this document is to
increase its familiarity and to answer important questions with regard
to the ISCO technique. In addition, the document must provide
sufficient information to start working with this technique as part of
in-house practice. The document translates knowledge often locked
up in complex and localised reports at a readable and applicable level.
It was decided to describe the different subjects on the basis of
1. IntroductionTable of Contents
1. Introduction 5
Book marker 7
Flow charts 8
2. ISCO and the commissioning party 11
ISCO remediation of pollution involving chlorinated 16 hydrocarbons underneath industrial premises
3. ISCO and the competent authorities 19
ISCO remediation involving aromatics / mineral 26 oil pollution underneath two residential homes
4. ISCO and the consultancy agency 29
ISCO remediation with permanganate 52 of residual pollution at a dry cleaner
5. Additional information 55
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ISCO - In-situ chemical oxidation
This document consists of three parts detailing information on the technique, each differing in information density and specifically geared to the three aforementioned target audiences. The first part is suitable for all target audiences in order to gain an overall picture of the technique. The parts written for the commissioning party and the competent authority are intended to provide a general picture of what is and what is not possible using in-situ chemical oxidation. The part for the consultant is a more in-depth discussion on the theory, the practice and the subject matter. Hence this part is three-tiered with the objective of providing sufficient information, so that the consultant is able to apply the technique in-house.
common issues. The subjects and questions are geared to the
different target audiences that may be confronted with the technique.
The target audiences that have been chosen for the document are:
• theproblemownerorthecommissioningparty;
• theassessororthecompetentauthority;
• theconsultantatasmallconsultancyagency.
The part of the document intended for the first target audience, the
problem owner or the commissioning party, discusses general matters
surrounding the technique. An example thereof includes the possible
effect which soil remediation using in-situ chemical oxidation can
have on operational management. The part aimed in particular at
the competent authority focuses on the various assessment aspects
involving soil remediation using in-situ chemical oxidation, including
the verifiability of the results that have been achieved. The third target
audience, consultants at smaller consultancy agencies, discusses the
technical aspects of the technique more. That does not mean that a
reader from a certain target audience is restricted. The document as
a whole offers a comprehensive picture of the technique and can help
explaining as to why a decision to use in-situ chemical oxidation is
made, or why it is decided against.
This document does not claim to be complete. As a result of research
and experience, gained when applying the technique at strongly
varying locations and pollutants, knowledge is still growing. This
document does provide an overview of the main aspects and know-
ledge at this moment in time and the application thereof in the field
of soil remediation in the Netherlands.
Each time the document discusses different applications of the
technique within in-situ chemical oxidation (ISCO), it will specifi-
cally state which application and thus which oxidant it involves.
Book marker
Flow charts
Figure 1 Decision chart for a fast, indicative assessment as to which ISCO remediation technique can be applied for a small to medium-sized source area;
Figure 2 Decision chart for a fast, indicative assessment as to which ISCO remediation technique can be applied for a small to medium-sized plume area;
A linear approach means that on a line at right angles with the plume, where the source area turns into the plume, a screen is placed with the stated ISCO technique.
Volume approach means that the entire plume is subjected to the so-called ISCO technique.
ISCO - In-situ chemical oxidation SKB Cahier
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11
ISCO - In-situ chemical oxidation
This part of the document is intended to provide a general picture of the technique. General questions such as: how does the technique work, what applications are categorised under ISCO and where can the technique be deployed are discussed in brief. Whilst writing this document, it has been taken into account that a company with a pollution problem may also be the possible commissioning party for ISCO remediation, hence subjects have been included that may affect opera-tional management.
How does in-situ chemical oxidation work?In the event of in-situ chemical oxidation (ISCO), a strong oxidant is
inserted in the soil in the form of a solid substance, diluted with water
or in conjunction with air. When the oxidant in the soil comes into
contact with the pollution, it is broken down chemically (oxidized)
producing harmless compounds, such as water and carbon dioxide.
Different oxidants are applied within soil remediation, for which the
process of degradation is either indirect, involving highly powerful
oxidation particles, or direct with the pollution, depending on the
oxidant. The different oxidants are discussed later in this document.
Which pollutants can be tackled?A large number of pollutants can be broken down using ISCO. Which
pollutants depends on the oxidant. The overview table (table 1) shows
which pollution can be removed using which oxidant. Less common
pollutants have not been included in the overview table, but may
be suitable for remediation by means of ISCO. A feasibility test
conducted by a specialised laboratory can offer a solution here.
Pollution in the soil often involves two different zones: a source area
and a plume area. A source area is characterised by high concentra-concentra-
tions of pollution in the soil and groundwater. Sometimes a source
ISCO and the commissioning party
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ISCO - In-situ chemical oxidation
1) This is the standard oxidation potential applicable at a pressure of 1 atmosphere, a temperature of 25°C and for 1 mol.
2) Persulfate can be activated by increasing the temperature or by using a catalyst.
Some oxidants also require certain auxiliary substances to be inserted
into the soil in order to ensure that the reaction produces to best
possible result. For example, in the event of Fenton’s reagent, an
iron solution is inserted in the soil, either as a salt, or as part of
a compound in an organic complexing agent. Persulfate performs
better when activated, i.e. the oxidation reaction needs a driving
force to gain momentum. Here too auxiliary substances are used.
As a result of the production process, permanganate contains small
amounts of impurities, particularly heavy metals. The concentrations
of both the auxiliary substances and the impurities are proportionally
small, so there is no renewed risk of pollution.
What is the effect of ISCO remediation on aboveground activities?Whether ISCO remediation affects aboveground activities depends on
the oxidant that is used, the manner in which the oxidant is inserted
into the soil and whether it involves remediation of a source or
plume area. In general, the inconvenience caused in the event of a
area of pollution also includes a pure product in the form of a so-cal-
led LNAPL (Light Non-Aqueous Phase Liquid), a layer that floats on
top of the groundwater table, or a DNAPL layer (Dense Non-Aqueous
Phase Liquid), that is heavier that water and that accumulates below
the groundwater table., Compared to the source area, the plume area
is characterised by lower concentrations in the groundwater and
hardly any or no pollution in the soil. ISCO can be applied both in a
source area of the pollution and in the plume area. The choice to use
a certain oxidant in a source or plume area depends on the location of
the pollution in the soil, the presence of pure product (NAPL), the du-
ration planned for a remediation and the costs. Some oxidants are too
expensive to use for low concentrations in a plume area. The overview
table (table 1) shows a summary which oxidant can be used where. An
overall assessment to establish this can be conducted by means of the
two flow charts (figures 1 and 2).
Which oxidants are used?A number of oxidants are used for the remediation of soil pollution.
In table 2, the different oxidants used for soil remediation in the
Netherlands to date have been ranked according to relative strength,
on the basis of the oxidation potential. The overview table (table 1)
includes a more extensive overview detailing the specific application
areas as well.
Persulfate has been included in both tables, as it offers a number of
advantages compared to the other oxidants. It has not yet been used
in the Netherlands. In addition, there are so-called fixed peroxides,
mainly originating from the detergent industry, which are used in soil
remediation on a gradually increasing scale. Both persulfate and the
fixed peroxides are not described in this document due to the limited
experience with these substances in the Netherlands.
Oxidant Relative strength Oxidation Condition potential (mV)1)
Fenton’s reagent Very strong 2.800 Liquid
Ozone/peroxide 2.800 Gas
Persulfate 2.700 (activated)2) Solid / Solution
Ozone 2.600 Gas
Persulfate 2.010 (not activated)2) Solid / Solution
Peroxide 1.800 Liquid
Permanganate 1.700 Solid / Solution
Fixed peroxides Weak - Solid
Table 2 The relative strength of the different oxidants.
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ISCO - In-situ chemical oxidation
Does ISCO involve substances that constitute a hazard?Yes, unless the contractor who carries out the ISCO remediation
is competent to do so. ISCO remediation does constitute potential
safety risks, as it involves working with strong oxidants, strong acids
or other chemical substances. All these risks can be controlled well,
provided the contractor is competent, complies with all safety regula-
tions that reduce the risks to an acceptable level and acts accordingly.
Supervision by an objective third party with regard to compliance
with the safety measures is part of the safe working practice during
an ISCO remediation. Once injected, the oxidants are used up in the
reaction which produces mainly water and carbon dioxide. Later in
this document, the safety aspects are discussed in greater detail.
Is it possible to be insured against ISCO remediation?Yes. The executive contractor must in any case have taken out liability
or CAR insurance. In addition, so-called BOSA insurance can be
taken out for any type of soil remediation, including ISCO remedia-
tion. This insurance reimburses specific soil remediation elements of
the activities. However, it is possible that the insurer sets additional
requirements with regard to the insurance. A case has been reported
that an insurer refused to insure remediation due to the presence
of cables and pipelines and the possible damage caused to them by
the oxidant.
remediation of a source area is more intense compared to that of a
plume area. Fenton’s reagent can cause some inconvenience in the
event of remediation of a source area, as the location which is injected
must be fully fenced off for multiple days securing access thereto.
This is done in connection with the possibility of violent under-
ground reactions occurring at the beginning of an injection. The
other oxidants offer multiple possibilities of inserting these in the soil.
For example, parts can be completed underground and with that the
inconvenience can be limited to a shorter period of time.
How long does ISCO remediation take?An attractive advantage of ISCO is the short period of time it takes to
complete the remediation, this in contrast to a number of alternative
soil remediation techniques. The time needed for an ISCO remediation
depends on the amount of pollution, the polluted soil volume, the
oxidant and the speed at which the oxidant can be injected. The first
two factors are site-specific . However, on the basis of the oxidant,
it is possible to indicate an average remediation time. An ISCO
remediation of a source area takes three months to two years. An
ISCO remediation of a plume area often takes longer. The overview
table (table 1) shows the average time period per oxidant in relation
to a remediation for pollution on a small to medium-sized scale.
How much does ISCO remediation cost?The general time needed to complete an ISCO remediation is difficult
to indicate. Assessing the costs of an ISCO remediation, without
taking into account the amount of pollution and the polluted soil
volume, is even harder. Per oxidant, the costs are determined by
different factors. With regard to permanganate, the main cost item
is the oxidant itself. More or less the same applies to ozone and
ozone/peroxide. In the event of Fenton’s reagent, the execution costs
account for the main cost item. Later in this document, the costs of
ISCO remediation are discussed in greater detail.
16 17
Fenton’s reagent, the groundwater pollution concentrations have
been reduced by 63 to 99%. The reduction has been established after
a period of approximately six months, after ending the active phase of
the test remediation. With regard to the ISCO test remediation using
ozone/peroxide, the groundwater pollution concentrations have been
reduced by 78 to 90%. After both test remediations have been carried
out, the groundwater concentrations appear the gradually increase
again. This indicates diffusion from the soil emerging from parts in the
ground which were not reached by the oxidant. The inflow of polluted
groundwater from other parts at the location causes the groundwater
concentrations to increase. The inconvenience caused to operational
management during both test remediations has remained limited to a
small surface area which did not affect corporate activities. Staff safety
too was sufficiently guaranteed during both test remediations thanks
to intensive process and risk monitoring.
ISCO remediation of pollution involving chlorinated hydrocarbons underneath industrial premises
Within the corporate grounds of a metal processing company in
the Dutch part of De Kempen (province of Noord-Brabant), pollution
involving tri-chloroethene (TCE) and 1,2-cis-dichloroethene (Cis) has
been detected. The corporate grounds include industrial premises for
production as well as storage. The industrial premises are used very
intensively. The pollution underneath the premises is diffuse and
present in concentrations of up to 1,000 µg·l-1 and in a number of
source areas up to a maximum of 30,000 µg·l-1 TCE. The pollution is
serious. Only Cis is present as a degradation product of the pollution.
Other degradation products which may demonstrate biological
degradation, vinylchloride, ethene and ethane, are not detected
onsite. No pure product is present.
In-situ chemical oxidation is quickly considered in view of the absence
of biological degradation. Within the framework of assessing the
remediation options, two remediation tests have been conducted
involving different ISCO techniques and in different source areas.
The techniques applied are the classic Fenton’s reagent and ozone/
peroxide. In addition to the feasibility of the ISCO technique, a lot of
attention has been paid to the inconvenience caused to the company,
staff safety whilst the techniques are applied and monitoring the
progress of the remediation. In the remediation test using the classic
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ISCO - In-situ chemical oxidation
This part of the document mainly discusses the ISCO remediation aspects which are important to the competent authorities. The competent authorities are particularly interested in finding out whether an ISCO remediation is feasible and whether the agreements entered into regarding the remediation are enforceable.
In order to assess the feasibility as well as the enforceability of a
remediation plan on the basis of ISCO, the following needs to be
taken into account:
• Istheresufficientinsightintotheamountofthepollution?
• Havelaboratorytestsbeencarriedoutdemonstratingthe
feasibilityofthetechnique?
• Hasaremediationtestbeencarriedout?Oristhisstilltobe
carried out to determine the final dimensions of the full-scale
remediation?
• Isthemonitoringprocesssufficientlygearedtotheendresult?
On the basis of the above questions, the competent authorities can
determine whether the feasibility and the technical options onsite
have been carefully considered. The questions do not specifically
apply to ISCO remediation alone, but more or less apply to all soil
remediation operations. When the technique is applied to reduce
the pollution load in a source area, ISCO deviates from other in-situ
techniques in terms of feasible remediation reduction values.
Monitoring is of vital importance for the feasibility. It is important for
the competent authority to carefully check the monitoring process, as
well as where and when monitoring takes place. In addition to these
two important aspects, a number of other issues are discussed in brief.
ISCO and the competent authority
3
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ISCO - In-situ chemical oxidation
More information on the different aspects with regard to the laboratory
tests and the remediation tests are included in chapter 4, ISCO and the
consultancy agency.
Is ISCO remediation feasible?The feasibility of ISCO remediation is determined by a multitude
of factors, as are all other in-situ techniques. Some of these factors
cannot be influenced, e.g. the soil structure. However, the influence
these factors have on the feasibility can be assessed prior to the
remediation being carried out. With regard to the different ISCO
applications, a laboratory test can assess whether the application of a
certain oxidant breaks down the pollution in a certain soil type. On
the basis of the laboratory test, an onsite remediation test can provide
insight whether the selected oxidant can indeed be brought into
contact with the pollution. In addition, realistic remediation reduc-
tion values are sometimes overstated in the light of a new technique
and people’s enthusiasm about it. The same applies to ISCO. Since
ISCO remediation is often aimed at the removal of the pollution
load, it is better to think in terms of the pollution load rather than in
remediation reduction values. The remediation reduction value must
be derived on the basis of the load removal which is deemed feasible.
With regard to all ISCO applications, the feasible load reduction
ranges between 70 and 95% or higher. However, in the event of a
volume reduction of e.g. 95%, the groundwater concentrations can
still exceed test or intervention values. Prior to the ISCO remediation,
there needs to be a general consensus on the load present in the
remediation area.
A feasible remediation reduction value?Is it possible to determine a feasible remediation reduction value for
ISCO remediation? Yes, however, traditional remediation reduction
values as target or intervention value are out of reach for nearly all
oxidants within the context of acceptable costs or efforts. This particu-
larly applies to the use of ISCO in source areas. A feasible remediation
reduction value can be derived on the basis of the load removal which
is deemed feasible, preferably on the basis of a remediation test.
Using the residual content value in the ground, the groundwater
concentration can be computed on the basis of balance calculation.
Using ISCO in plume areas involves much lower starting concentrations
and it is therefore easier to derive a feasible remediation reduction
value on the basis of a test remediation. Here too a target value is
highly unlikely to serve as a feasible remediation reduction value.
Even here, the remediation return value cannot be reached in some
areas of the remediation area, despite all efforts. In that instance a
so-called polishing step can be applied. By using an alternative
oxidant, which stays in the ground longer, the pollution can be broken
down gradually. Permanganate can be used after the application of
a Fenton’s reagent ISCO remediation in order to break down any
residual chlorinated hydrocarbons. In the event of pollution with
mineral oil, fixed peroxides can be applied. This results in oxygen
being produced followed by biological degradation of the residual
pollution.
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ISCO - In-situ chemical oxidation
which the effects of diffusion from the soil will manifest itself
much later. Also, in the event of agreements on when to determine
whether remediation reduction values have been achieved, the
stability of the different oxidants in the ground needs to be taken
into account.
Chapter 4 details further information on the different aspects with
regard to monitorin
Is inconvenience caused to other aboveground activities?One of the tasks of the competent authorities is to find out whether an
ISCO remediation causes inconvenience to other aboveground activi-
ties in the direct vicinity of the remediation site. Practical examples:
• Threatenedactivities,suchasgroundwaterextraction,canbe
negatively influenced by ISCO remediation. For example,
permanganate colours the groundwater dark purple, a harmless
yet often undesired side-effect.
• Construction.Evaporationofhazardoussubstances,including
both reaction products and pollution, towards surrounding
buildings, is possible. The set-up can take this into account
and reduce any potential risks, e.g. by installing a ground air
extraction system.
• Productionprocess.Disruptionoftheproductionprocesscan
occur if remediation takes place within a company. The commis-
sioning party is not always the owner of the company where the
remediation is to be carried out.
Is the ISCO remediation enforceable?ISCO remediation can be enforced by the competent authority by
carefully checking the monitoring data. Within this respect, the final
concentrations achieved must be noted in particular, as diffusion
from the soil may still occur.
It may be the case that during the remediation not all onsite pollution
has been reached by the oxidant. This may be the result of incomplete
dimensioning;toolittleoxidantmayhavebeeninjectedinorderto
remove the load, or the pollution has partly shifted as a result of the
injection. It is these points that the competent authorities can enforce.
In addition, it is important to the competent authorities that safety is
taken into account. To this end, continued process monitoring can
be used.
The competent authorities are able to enforce at the following points:
• Inordertocheckwhetherallpollutionintheremediationarea
has been removed, measurements must not be conducted in
the injectors alone. Particularly in the injectors, contact between
the oxidant and the pollution has been intense, hence monitoring
must be performed predominantly in newly placed monitoring
wells;
• Inordertodeterminewhetherthepollutionhasshifted,moni-
toring must be effected both upstream and downstream during
injection and rest periods of ISCO remediation operations. It is
further recommended to check the edges of the pollution.
• Duringtheinjectionoftheoxidant,forreasonsofsecurity,the
groundwater level must be measured, the temperature and the
formation of explosive gases expressed as the LEL value (lower
explosion limit). If it appears that gas formation is excessive, any
risks can be assessed on the basis of indoor air measurements
within surrounding buildings.
• Whenmeasuringthediffusionfromthesoil,thestabilityofthe
different oxidants in the ground needs to be taken into account.
In the event of Fenton’s reagent, the diffusion from the soil can
be quickly checked as peroxide will disappear from the soil fast.
Permanganate is much more stable in the ground, as a result of
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ISCO - In-situ chemical oxidation
• Otherpossibilitiesofcontactwiththesurroundings.This,for
example, is possible due to the quick rising of the groundwater
level whilst the oxidant is being injected. In the event of a rise in
the groundwater level, the surrounding area may come into
contact with the polluted groundwater or the oxidant itself.
• Diversions.When,forexample,thepollutionislocatedunder-
neath a road surface, traffic during the injection period is not
desirable from a safety point of view.
• Ecology.Whenataremediationsitefloraorfaunaareprotected,
additional protective measures may be taken. In a case involving
protected trees near the remediation site, additional ground air
extraction filters were placed in combination with intensive
monitoring to prevent any damage.
Does chemical oxidation require specific permits?No. In the event of short-term remediation operations (less than six
months) within grounds for which no permit has been issued within
the framework of the Environmental Management Act, the instal-
lation used to insert the oxidant in the soil is not deemed a facility.
However, since ISCO remediation involves the storage of hazardous
substances, remediation operations that take longer do require a
permit. When the installation is used on corporate grounds for which
a permit has been issued within the framework of the Environmental
Protection Act, a written notification of the activities by the permit
holder suffices. This must be done at least one month in advance.
In addition to the Environmental Protection Act, other permits may
apply in the event of ISCO remediation. Experience shows that the
permits have been requested in some of the following cases:
• ExemptionfromtheWaterBoardortheHigherWaterBoardfor
the installation of monitoring wells and injectors.
• ExemptionfromtheWaterBoardortheHigherWaterBoardfor
the injection of a liquid.
• PermitunderthePollutionofServiceWatersActwhenextracting
and discharging groundwater at the same time.
• Apermitforthestorageofchemicalswithinpublicgrounds.
An ISCO remediation must of course also be reported to the
competent authorities prior to the start of the remediation. In some
cases the same applies to remediation tests.
26 27
was injected during two injection periods. After the first injection
period, the groundwater concentrations with pollution were reduced
by more than 90%. Following the second injection period, approxi-
mately 4 weeks after the first period, the groundwater concentrations
were reduced to the desired concentration of 65 µg·l-1 for benzene.
Intensive risk monitoring was carried out during the active remedia-
tion period. During those periods, the LEL value was not exceeded
and no increased concentrations of oxygen, mineral oil or volatile
aromatic hydrocarbon were measured in the crawl spaces underneath
the houses. After twelve weeks, a monitoring round was conducted
to determine the diffusion from the soil. It was found that the BTEX
concentrations had increased as a result of diffusion from the soil.
The overall reduction of the groundwater concentration was still more
than 90%. Immediately after the ISCO remediation, a positive side
effect was detected in that the redox conditions in the groundwater
had risen from low oxygen content to high. This is favourable to the
biological degradation of the residual pollution. A final monitoring
of the crawl spaces to determine any public health risks is still to be
carried out.
ISCO remediation involving aromatics/ mineral oil pollution underneath two residential homes
In the past, an oil tank was once stored near two residential homes in
a city in the province of Overijssel. Although the oil tank was removed
prior to the houses being constructed, part of the pollution remained
in the soil. The soil contained mineral oil pollution causing high
concentrations of volatile aromatic hydrocarbons (BTEX) in the
groundwater of up to 26.000 µg·l-1. Since BTEX groundwater pollution
involves a direct risk to public health and thus the residents, it
was decided to carry out a specific remediation of the soil. When
considering the different remediation options, during which an in-situ
remediation was preferred with a view to the presence of the houses,
an ISCO remediation using the classic Fenton’s reagent proved to
be the most favourable choice. During the assessment, the short
remediation time and with that the short period of inconvenience
for the residents played an important role. The remediation plan
linked a load removal of at least 80% to a desired groundwater
concentration of 65 µg·l-1 or lower per individual component.
It was decided not to do a test remediation, but to carry out a full
remediation directly. In addition to the elaborate system for the
injection of the oxidant, a ground air extraction system was installed
against the front of the houses. Approximately 3 m3 of 50% peroxide
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ISCO - In-situ chemical oxidation
4.1 ISCO in theoryPrevious parts of this document outlined the principles of the techniques, the different oxidants and applications and the type of pollutants that can be removed with it. This part of the document elaborates on this information and describes the chemical operation of the different oxidants. An overview of this information is detailed in table 1. In table 2, the oxidants are arranged according to relative strength. The choice as to where to deploy the oxidant, either in the source area or the plume area, can be made on the basis of the two flow charts (figures 1 and 2).
Which oxidants are used?
Fenton’s reagentFenton’s reagent is the strongest oxidant currently used within soil
remediation. Fenton’s reagent is a combination of hydrogen peroxide
and iron (II). The iron (II) serves as catalyst and can be added to the
soil in two different ways. In what is commonly referred to as the
classic or acid Fenton’s, iron (II) is added in the form of an iron
sulphate solution, whilst the soil must be acidified with a strong acid
in order to maintain the iron (II) solution. During the application
referred to as modified Fenton’s, the iron is added together with an
organic complexing agent. In this instance, it is not necessary to
acidify the soil. This at the same time prevents the risk of heavy
metals being mobilised, which risk is present within the classic
application. The complexing agent used in the United States is called
EDTA. Its use is banned in the Netherlands. In the Netherlands, a
number of contractors use citrate as complexing agent. The peroxide
in either ISCO application with Fenton’s reagent is a concentrated
solution of 35 to 50%, which is diluted to a peroxide solution of
5 to 15%. Degradation of pollution using Fenton’s reagent takes place
ISCO and the consultancy agency
4
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PersulfateThe application of persulfate is two-tiered: non-activated and
activated. Non-activated persulfate is a mild oxidant and not applied
in soil remediation. However, in its activated form, it is as nearly as
strong an oxidant as ozone/peroxide and Fenton’s reagent. Activation
means that the chemical oxidation reaction is catalyzed forming both
hydroxyl and sulphate radicals. Activation can be done in four ways:
1) adding heat (up to 45oC), 2) adding a catalyst such as iron (II),
3) adding a complexing agent such as EDTA or 4) strongly alkalyzing
the ground (up to a pH of 11.5).
Persulfate in the ground is very stable and stays in the ground for
a number of months, depending on the ground and the pollution.
In addition, persulfate can be used to break down a wide range of
pollutants. These possibilities are already applied in the laboratories
and in the United States too the oxidant is already in use. Persulfate is
listed in the overview table (table 1) and table 2, despite the fact that it
has not been used in the Netherlands to date. Persulfate has a number
of advantages over other oxidants and expectations are that in the
Netherlands too it will be applied within the foreseeable future.
Since there is not much experience with the use of persulfate as yet,
this oxidant is not discussed any further.
OzoneAs is the case with Fenton’s reagent, ozone can react with the
pollution directly or via hydroxyl radicals that have been formed.
Oxidation by radicals is faster than oxidation by ozone itself.
However, the reactive potential of ozone is such that it may not be
transported. Hence all oxidant that is used at the location must be
produced onsite. However, this is compensated by the fact that ozone
(because it is a gas) is the only oxidant that can be used in unsaturated
parts of the soil. The stability of the oxidant in the ground is one to
two days, comparable to that of ozone/peroxide. Ozone has been
on the market as an oxidant as the C-SpargeTM technique in the
Netherlands for some years now. As is the case with ozone/peroxide,
during this application the ozone is mixed with air prior to being
injected.
on the basis of a direct chemical reaction or via so-called hydroxyl
radicals. As a result of this combination of reactions, the degradation
is fast and effective, yet not particularly specific. Everything in the soil
that can be oxidized is oxidized. Therefore, Fenton’s reagent is able to
break down a wide range of organic compounds. Since the reaction
is fast, the injection of the oxidant and the auxiliary substances
often take only a few days or weeks. The amount of Fenton’s reagent
injected on a site depends on the oxidation potential of the soil, the
pollution and the load. An ISCO remediation with Fenton’s reagent
is carried out on the basis of at least a laboratory test in which both
factors are determined. In the event of the classic reagent, it is also de-
termined which acid must be injected and the amounts thereof. Once
injected in the soil, the stability of the oxidant lasts less than a day.
Ozone/peroxideOxidation of pollution on the basis of a combined injection of liquid,
peroxide and a gas, ozone, has been applied in the Netherlands since
only recently and is marketed as PerozoneTM. The mixture of peroxide
and ozone is a stronger oxidant compared to either individually.
The ozone/peroxide mixture, within which ozone is first mixed with
air, is injected in the soil via specially designed injection nozzles. As is
the case with Fenton’s reagent, degradation takes place via hydroxyl
radicals causing a fast, yet not specific breakdown. Hence ozone/
peroxide can be used for a wide range of pollutants. Once injected
in the soil, the stability of the oxidant lasts around a day, maximum
two days.
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What is the effect of ISCO remediation on the soil?During ISCO remediation pollution is broken down, or in other
words: oxidized. As a result, the soil conditions become more oxic,
meaning the oxygen content increases, whereas in the Netherlands,
particularly a few metres underneath groundwater level, the soil is
often anoxic or low in oxygen content. When using Fenton’s reagent,
peroxide and ozone, the oxygen concentration in the groundwater
rises to the extent that it can have a positive effect on the biological
degradation processes. However, downside is that bacteria also
consist of organic material and are thus also oxidized. Yet after
ISCO remediation, the soil is not biologically dead. Within the soil,
extremely small pores cannot be accessed by the oxidant and bacteria
are able to survive therein.
In addition to the soil becoming more oxic, the application of any
oxidant involves the formation of acid causing the pH of the soil
and the groundwater to fall. In the event of pollution involving
chlorinated hydrocarbons, this effect is more intensive as hydro-
chloric acid (HCl) is formed. However, in the event of classical
Fenton’s reagent, the pH is reduced in order to improve the chemical
oxidation reaction. The reduction of the pH has an unfavourable
effect on the behaviour of metals, as at low pH values the mobility
increases. These processes need to be taken into account, particularly
so when in addition to organic pollution, the pollution includes heavy
metals. The mobilisation is often short-lived, after the active phase
of the ISCO remediation the mobility falls again. In the event of
permanganate, you need to be vigilant for heavy metals in the oxidant
itself as a result of the production process. Special permanganate,
with low contents of heavy metals, is available for soil remediation
applications. The application of permanganate in laboratory tests
has led to a reduction in permeability of the soil as a result of the
formation of manganese oxides (also referred to as black manganese).
This has not been detected in the field with regard to the use of
permanganate solutions of up to 4%.
In the field, it has appeared that the use of Fenton’s reagent can
considerably increase the permeability of the soil. The Fenton’s
reagent oxidizes organic substances and thus increases porosity,
which leads to a higher permeability of the soil. The advantage is
PermanganatePermanganate is a mild oxidant, but in contrast to the aforemen-
tioned oxidants, the degradation reaction is very specific. For
example, to break down double carbon compounds found in
many polluted grounds, such as tetrachloroethene (also known as
perchloroethene, PCE) and degradation products in the ground. In
addition, the stability of the oxidant in the ground is high. Depending
on the ground and the pollution, permanganate can continue to be
reactive for multiple weeks and break down the pollution.
Permanganate can be applied in multiple formats. The most common
forms are potassium and sodium permanganate. The advantage of
sodium permanganate is that it can be supplied as a solution.
A standard 40% solution is available to the soil remediation market,
with low concentrations of heavy metals and impurities (RemOxTM).
Potassium permanganate is cheaper, yet only available as a solid.
Therefore, in order to inject it, it needs to be dissolved which brings
a number of adverse side effects such as dust formation. Also, the
maximum solubility of potassium permanganate is lower (solubility
of approximately 6%) compared to that of sodium permanganate.
All permanganate solutions are dark purple in colour.
Fixed peroxidesFixed peroxides include all compounds such as calcium and magnesi-
um peroxide and magnesium percarbonate. They are compounds that
have been used in cleaning products and detergents for some time
now. In the soil remediation sector, fixed peroxides are often referred
to under the generic term of oxygen release compounds (ORC®).
Fixed peroxides are often mild or even weak oxidants and generally
used to add oxygen to groundwater to stimulate aerobic biological
degradation. The oxidation potential of fixed peroxides is often not
enough to oxidize pollution directly. The principle and application
possibilities of fixed peroxides are not discussed any further in this
document.
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• Permeabilityofthesoil The more permeable the soil, the better. In highly permeable soil,
the oxidant will distribute better and more evenly than it would
in low permeable soil.
• Groundwaterlevel Since liquids or gases are injected during ISCO, the injection
requires a certain counter pressure due to the soil and ground-
water column. If the groundwater level is below 1.5 m -mv, there
is not enough counter pressure, making injection impossible. If
groundwater levels are low, there is also a chance of the ground-
water rising as a result of injection, increasing the risk of a flood.
If there is a cover, e.g. paving, at ground level, it may be possible
to work even though the groundwater level is low.
• Oxidantconsumptionofthesoil The oxidants used in soil remediation are usually not very
specific as to what they oxidize. It is important to know how
much oxidant the soil will consume, so that a sufficient amount
can be injected in order to oxidize the pollution as well. With
any oxidant we recommend determining the soil consumption
on the basis of a laboratory test prior to ISCO remediation. Soil
parameters that are important to determine ISCO remediation
in advance are: the level of organic material, chemical oxygen
demand (COD), and natural soil oxygen demand (NOD). Not all
parameters are of importance to all applications of ISCO.
• Buffercapacity Especially when using classic Fenton’s reagent it is important to
know how much acid must be injected to create the best possible
circumstances for the oxidation reaction. This buffer capacity
is determined by the presence of carbonate and the pH level of
the groundwater.
that the oxidant distributes better in the soil. Disadvantage is that
in a soil with a high content of organic substances, violent reactions
can occur, causing an excessive increase in soil temperature and
unacceptable safety risks. All oxidants oxidize organic substances
and thus in addition to violent reactions, there is also the risk of
subsidence in the presence of layers of peat. However, subsidence can
also occur in the event old wooden foundations are present in city
centres. Other underground infrastructure too, such as cables and
pipelines can be affected.
4.2 ISCO in practice
A consultancy agency only needs to know how a technique works
and for which pollution it can be used. There is a wide range of
techniques, including in-situ remediation techniques which offer
the same solution. This section of the document describes practical
matters required to compare the application of ISCO with other
remediation options.
Which soil parameters determine the feasibility of ISCO?In order to answer the question whether remediation with ISCO in a
certain location is feasible, we need information about the soil para-
meters listed below.
• Soilstructure The most important aspect in ISCO remediation is bringing the
oxidant and the pollution into contact with each other. Although
there is no such thing as homogenous soil, soil consisting mostly
of highly permeable sand is more suitable for an in-situ remedia-
tion than soil that consists of a succession of sand and clay.
The more varied or heterogeneous the soil structure, the easier
the application of ISCO. Preferred channels are created quicker in
heterogeneous soil, so the oxidants injected will not reach part of
the pollution.
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• Undergroundinfrastructure In the Netherlands, especially in urban areas, this forms part of
the soil parameters. The risk of preferent flow paths is larger and
the chance of reaching the pollution diminishes along under-
ground infrastructure such as cables/pipes, but also concrete
foundations.
Within the framework given below, the range within which certain
soil parameters can occur in order for them to be applied is given for
all different oxidants.
Fenton’s reagentOxidation with the classic version of the Fenton’s reagent is the most
effective under acidic circumstances, - pH between 2 and 4 - but can
be used up to a pH of 7. If the pH is higher than 8 it is not useful to
use the classic form of Fenton’s reagent. This is due to the iron(II) that
acts as a catalyst in classic Fenton’s reagent and which must be kept
soluble. If the pH exceeds 7, peroxide breaks down and too little is
used for the oxidation reaction. If the pH is even higher, combined
with high carbonate concentrations in the groundwater, the hydroxyl
radicals are absorbed by the carbonate. In the neutral version of
Fenton’s reagent, the pH levels and presence of carbonates play a less
determining role, since the iron(II) is kept soluble by the complexing
agents. Before starting ISCO remediation with Fenton’s reagent, you
must determine the oxidant consumption of the soil.
Ozone and peroxide/ozoneLike the classic Fenton’s reagent reactions, ozone reactions are the
most effective in an acidic environment due to the formation of
radicals. Since ozone is injected as a gas, oxidation with ozone is also
an option for ISCO in the unsaturated zone. When applying in the
unsaturated zones, it is important to take note of the humidity levels.
In the unsaturated zone, ozone distributes better in low humidity
levels compared to high humidity levels. When applying ozone in
the saturated zone, preferent flow paths caused by underground
heterogeneous activities are created quicker, because the gas moves
upwards and soil usually has a horizontal stratification. For both ozone
and ozone/peroxide, the oxidant consumption by the soil is of minor
importance, and in general no laboratory tests are carried out to
determine this. As a rule, every m3 of soil consumes approx. 15 g
of ozone. The ideal pH level is between 5 and 8. A pH level of 9 is
regarded as the upper limit.
PermanganatePermanganate can be applied in a broad pH range. However, per-
manganate is susceptible to the soil structure, since the oxidation with
permanganate creates manganese dioxide (also called brownstone),
as a result of which permeability can decrease if the pollution load is
high. With permanganate it is essential to carry out a laboratory test
prior to the remediation in order to determine how much oxidant the
soil consumes. This is a so-called natural soil oxygen demand (SOD
or NOD) test. The NOD of soil depends on the permanganate concen-
tration under which the test is carried out. This means the test must be
carried out under multiple permanganate concentrations, including
the concentration under which the remediation is carried out. A rule
of thumb is that when the NOD value exceeds 2 g MnO4·kg-1 of soil,
the application of permanganate is no longer cost-effective. In the
United States, the results of a laboratory NOD test are often corrected,
because the contact between oxidant and soil is often better than
it is in the field. Such a correction does not seem justified in the
Dutch situation.
• Pollutionload Strictly speaking it is not a soil parameter, but it is important
when determining whether ISCO remediation is worth conside-
ring. Since most oxidants are extremely suitable for removing the
bulk of the pollution, it is important to know what the pollution
concentrations are and whether there is any pure product or not.
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What determines the effectiveness of ISCO remediation?The effectiveness and success of ISCO remediation are determined by
the contact between the oxidant and the pollution. In order to bring
the oxidant and the pollution into contact effectively, an injection
system geared to the location-specific circumstances is required.
A proper characterisation of the location, soil structure and the
aforementioned soil parameters and the demarcation of the pollution
are very important. In addition, it is important to make a good
assessment of the pollution load and the soil’s demand for oxidant,
since the amount of oxidant to be added depends on this.
In order to obtain clarity about the extent of contact between the
oxidant and the pollution and the amount of oxidant required, a
number of laboratory tests must be carried out prior to a full-scale
remediation. It is also recommended to carry out a test remediation
(a small-scale field test), especially in the case of major pollutants.
Based on both results, the cost effectiveness of a full-scale ISCO
remediation can then be determined.
What is the environmental outcome of ISCO remediation?The environmental outcome of remediation is determined by a
number of factors. In the case of ISCO remediation, the following
factors could affect the environmental output:
• Releaseofdangeroussubstances The oxidation of pollution mainly generates water and carbon
dioxide. In principle, no dangerous substances are released.
It is possible that the chemical breakdown of the pollution is
accompanied by the production of heat, causing the soil to warm
up slightly up to approx. 30°C. This may cause the pollution
to evaporate.
• Productionofwastematter In order to prevent exposure to any pollution caused by
evaporation, a ground air extraction system is installed for nearly
all oxidants (with the exception of permanganate). The extracted
air must be purified, during which active carbon is produced as
waste matter.
The applicability can then be determined on the basis of
the following:
• ISCOremediationisapplicableif: - thepollutioncanbeoxidizedwithoneoftheoxidants;
- the hydraulic permeability of the soil exceeds 10-6 cm
persecond;
- thegroundwaterisdeeperthan1.5m-mv;
- It is not a problem if pure product is present, provided any
LNAPL layer is not thicker than 15 cm.
• ISCOremediationisnotapplicableif: - thepollutioncannotbeoxidizedwithoneoftheoxidants;
- the soil structure shows that the pollution can mainly be
found in a layer of soil with a high level of organic com-
pounds,e.g.peatorhighlyhumoussoil;
- there is a LNAPL layer thicker than 15 cm. If the LNAPL layer
is thicker than 15 cm, we recommend removing the LNAPL
layerbymeansofadifferenttechnique;
- there is any pure product in the vicinity of the underground
infrastructure, e.g. cables/pipes.
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We should emphasise that the prices listed in the table are not fixed.
It is merely an estimation of the costs. The actual costs strongly
depend on the location-specific circumstances and the type of
pollution, and may therefore deviate from the table. The estimated
price per m3 of soil does not include the costs for the environmental
supervision and management.
How does ISCO compare to other in-situ remediation techniques?ISCO is an in-situ remediation technique which can be applied
both in the source area and in the plume area of the pollution.
In the Netherlands, this technique is mainly used as a source removal
technique. Table 4 shows how ISCO remediation compares to other
techniques for polluted source areas without pure product.
• Groundwaterextraction In order to enable the oxidant to come into contact with the
pollution as well as possible, groundwater can be extracted in
specific locations. This means that injections are carried out at
one point and that a similar amount of groundwater is extracted
at one or more other points. This enables one to control the
distribution of the oxidant. When extracting groundwater,
a drop-out current of polluted groundwater is created. This
groundwater must be treated before it can be discharged.
• Wateruse The water use - either tap water or extracted groundwater -
strongly differs per oxidant. During the injection of Fenton’s
reagent and permanganate, a relatively high amount of water is
used in order to dilute the injection products. However, only
small amounts of water are needed for the injection of ozone and
ozone/peroxide.
• Energyuse The energy use during ISCO remediation strongly differs per
oxidant. Energy use during the injection of Fenton’s reagent or
permanganate is low. When using ozone and ozone/peroxide,
ozone must be generated locally, so the amount of energy used
is higher compared to the other versions.
How much does ISCO remediation cost?In the first section of the document we briefly discussed the costs
of ISCO remediation in general. In the case of permanganate, the
biggest cost item usually is the oxidant itself. To some degree, this also
applies to ozone and ozone/peroxide. In the case of Fenton’s reagent,
the execution costs are the biggest cost item. Table 3 shows indicative
prices, based on a number of large and small-scale ISCO remediation
projects using different oxidants. The basic cost price of the oxidant
is also included, i.e. without the costs relating to an injection system,
execution costs, etc.
Oxidant Price per m3 of soil Cost price Type (e) (e/kg)
Fenton’s reagent 15 - 120 0,7 - 1 5 - 15% solution
Ozone/peroxide 2 - 20 plume method 1 - 1,5 Gas/liquid
20 - 60 source method
Ozone 40 - 60 1 - 1,5 Gas
Permanganate1 25 - 100 4 - 6 40% solution
Table 3 The indicative price per cubic metre of polluted soil and the cost price for the different oxidants.
1 Sodium permanganate-based
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The table only serves as an indication as to how the different tech-
niques compare. Compared to the other techniques, the biggest ad-
vantage of ISCO is the short remediation period at relatively low costs.
The environmental output of the technique is also high compared to
for instance groundwater draw-off (pump and treat) or compressed
air injection. On the other hand, the level of disruption during ISCO
remediation can be higher than the other techniques. However, this
does depend on the type of oxidant used. The main argument against
quick ISCO remediation is that one is left with residual pollution in
the case of remediation of a source area. This must subsequently be
reduced in concentrated form by means of a different technique, e.g.
stimulated biological degradation.
4.3 ISCO and the design
The knowledge of the technique and the decision whether or not
to apply ISCO to a location was discussed in previous paragraphs.
Now it is time to focus on the subjects relating to the design. This
section of the document describes subjects required to be able to
assess the design from a contractor, to supervise the project and to
test the results.
What are the main design parameters and how can I determine these?Many of the design parameters for ISCO remediation are similar to
the aforementioned soil parameters to determine the feasibility of
the remediation. In addition to these parameters, a number of design
parameters must be set for the injection system.
• Horizontaldistancebetweentheinjectionpoints The distance between the injection points is determined by the
projected effective radius. The effective radius depends mainly
on the soil structure and the injection depth. As a rule of thumb,
the 15 feet rule is applied, i.e. the injection points are placed at a
maximum distance of approx. 5 m. Larger effective radii are used
for ozone and ozone/peroxide, ranging from 10 to 20 m.
• Depthoftheinjectionpointfilterarrangements This is entirely determined on the basis of previous research data
and the soil structure. In addition to horizontal permeability, the
soil also has vertical permeability. The filters are to be positioned
in such a way that the entire polluted soil section comes into
contact with the oxidant.
• Howmuchoxidanttoinject The amount of oxidant to be injected consists of the amount of
pollution load present plus the amount of oxidant consumed by
the soil. The first can be determined on the basis of the chemical
reaction between the oxidant and the pollution when the extent
of the pollution load is known. The consumption by the soil can
be determined in advance by means of a laboratory test of soil
samples. The organic content and COD can also be used for this.
For Fenton’s reagent one must also take into account the fact that
out of the amount of peroxide injected only 10 to 20% is actually
involved in the reactions.
ISCO Pump Compressed Stimulated bio- and treat air injection logical degradation
Remediation Short Very long Long Long
period <5 years >30 years <10 years >10 years
Cost level Low High High Low
Disruption Depends on None Little None
application
method
Environmental High Low Low High
output
Table 4A relative comparison of different in-situ remediation techniques.
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• Whatarethedistributionpictureandtheinfluenceofthesoil
structure,forinstanceintheeventofpreferentflowpaths?
• Whatisthemaximumloadreductiontobeachieved?Arethe
remediation reduction values for the full-scale remediation
feasiblewiththeintendedsystem?
• Howmuchoxidantandauxiliarysubstancesarerequiredin
ordertoachievethedesiredloadreduction?
• Whatisthecompositionofthepollutionafterthetest
remediation?Hasthepollutiontrulybeenbrokendown,
orhastheinjectionmerelyshiftedit?
• Isthereanydiffusionfromthesoilafteran(initial)
injectionphase?
• Istheselectedoxidantcost-effective?
For a proper test remediation, the objectives and questions to be
answered by the test are to be recorded. Intensive monitoring of the
injection system and the results in the soil are vital during a test
remediation, because this data provides the answers to the questions.
A test remediation does not necessarily have to be successful in order
to meet the formulated objectives. A failed test remediation often
teaches us more than a successful one. In both cases it can save the
commissioning party a lot of money.
As is the case with a full-scale remediation, a test remediation
requires a decision and report from the competent authorities.
The risks and safety measures involved in ISCO remediationNo remediation is without risks. However, the risks can be controlled
if you have a thoroughly experienced consultancy agency, contractor
and possible subcontractors, combined with a proper risk inventory
carried out prior to the ISCO remediation. An ISCO remediation can
involve a multitude of different risks, with health and safety risks
taking absolute priority. In addition there could be ecological and
quality risks. We will not discuss the latter two.
• Dailyinjectionquantities The amount to be injected daily determines the remediation
period and with that largely, the costs. For highly permeable soil,
the injection quantities for Fenton’s reagent and permanganate are
approximately 1 to 1.5 m3 of undiluted solution.
The design parameters can be obtained:
• bycombiningchemicalanalysesandgeohydrologicaldatafrom
the preliminary research with a possible additional soil survey,
aimed at the execution of the remediation. Based on this data,
the general applicability of ISCO can be determined.
• bymeansofspeciallaboratorytest,includingcolumnandbatch
experiments, in order to check the applicability and to verify
or substantiate certain assumptions for the application of the
technique. This could include an NOD determination prior to
ISCO remediation with permanganate.
• bymeansofatestremediationonlocationinordertodetermine
the applicability under location-specific circumstances and
important parameters for the design of the full-scale remediation.
Is a test remediation required?Yes, in principle one must carry out a test remediation prior to any
in-situ remediation technique. No matter how much experience the
consultancy agency and the contractor may have, no location is the
same and the design parameters can differ considerably per location.
Based on the results of the test remediation, the design parameters
can be determined and optimised. This will lead to an improved
remediation system, optimisation of the costs - including those of
the full-scale remediation - and with that to an increased chance of
success for the ISCO remediation.
The results of an average test remediation should answer the following
questions:
• Whatistheeffectiveradiusoftheinjectionpoints,bothhorizon-
tally and vertically, and with that the distance required between
theinjectionpoints?
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Safety measures for a number of ISCO-specific subjects:
• Oxidantsareusuallydilutedontheremediationlocationitself,
using a concentrated solution supplied by a manufacturer. The
chemicals must be diluted in a designated process container which
can be sealed off properly. The same applies to the production of
ozone on location. In the case of permanganate, a special section
of the location can be set up for the preparation of the injection
solutions.
• Theoxidantsaretobestoredinaproperlysealedcontainerfitted
with precautions such as drip-trays so that the substance cannot
spread in the event of calamities.
• Onlyappropriatelyqualifiedandexperiencedstaffcanbe
deployed for injection activities.
• Duringtheinjectionoftheoxidants,twomembersofstaffmust
be present at the location at all times.
How do I select a contractor?A contractor who tenders for an ISCO remediation should first and
foremost be able to demonstrate that he has experience with the
technique. Working with a chemical oxidant is not without risks.
It is therefore important that the level of experience of the contractor,
and any subcontractors, is sufficient. The level of experience can be
demonstrated by, among other things, reference projects, but also by
the required accreditation and certification of the company itself or
the equipment to be used. There are a host of other possible things
that may be taken into account in the selection including, not least,
the price.
A small selection of criteria that may not be obvious, but are
important:
• Thepositioninganddesignoftheinjectionsystemandthe
amounts one thinks can be injected. Does it involve one or more
injectionroundsofoxidant?Ifso,whatcriteriaformthebasisfor
anewinjectionround?
• Havetheresultsfromthepreliminaryinvestigation,including
laboratory tests, been included and actually incorporated in
theresult?
Since use is made of chemicals that harm man’s health, an ISCO
remediation involves certain health risks. As for toxicity, oxidants
such as peroxide and permanganate are relatively safe. The dangers
involved in oxidizing chemicals must be acknowledged and kept to a
minimum. Contact with the skin and inhalation of these substances
must be avoided at all times. Furthermore, the oxidants should never
be mixed with reducing substances and inflammable substances.
Oxidants and reducing and inflammable materials react strongly.
The reaction generates oxygen, which has fire-inducing powers.
High concentrations of ozone in the air - more than 2 ppm - can lead
to irritation of and damage to the eyes and airways. Air with high
levels of ozone can build up in enclosed areas or in a space where
remediation is carried out. It is vital to properly ventilate enclosed
areas or spaces. Detection equipment will be installed to detect any
early-stage build ups. In addition, all ignition sources are to be kept
away from the equipment used.
The safety measures for an ISCO remediation are very similar to any
other remediation. The standard safety measures for the execution of
a remediation are described in the CROW publication 132. A health
& safety plan must be drawn up prior to an ISCO remediation, inclu-
ding the test remediation. Also, the injection equipment is to be tested
for any faults and the effects thereof by means of a so-called HAZOP.
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• Theconfirmationofinjectedvolumes,flowratesandcontractions
ofoxidant;
• Measuringthestabilityoftheoxidantinthesoil;
• Measuringoxidantconcentrationsinthegroundwaterorground
air samples.
When oxidants are used, process monitoring comprises the measuring
of the pH, temperature, pressure, oxygen and carbon dioxide concen-
trations. These parameters - to monitor the process - are measured
very frequently each day. The pollution in the soil, groundwater and
ground air is measured on a less frequent basis. In addition, it is im-
portant to find out if there are any preferent flow paths , and to assess
how the oxidant and any other substances required distribute them-
selves. To that end, monitoring wells can be fitted afterwards in order
to determine whether the entire remediation area has been treated.
Since powerful oxidants are used, so-called risk monitoring is to
be carried out as a safety measure in built-up locations. Parameters
such as temperature, oxygen, pressure, etc. are measured each day
on a regular basis, e.g. each hour or every three hours following the
last injection of oxidant for that day. The measurement is preferable
carried out in the open air. This is especially important during ISCO
remediation with Fenton’s reagent. If ozone is injected, the ozone
concentration is also measured. If an air soil extraction system is in
place, the build-up of hazardous substances (photometric ionisation
detector, or PID measurement) and explosive gases (lower explosion
limit, or LEL measurement) is checked in the extraction system.
Permanganate is a milder oxidant and will therefore carry fewer risks,
as a result of which risk monitoring will be simpler.
In some cases, risk monitoring can also comprise the effects of
chemical oxidation on the biological life in the soil. To that end,
bacteria counts can be carried out.
A couple of weeks after the injection phase, performancemonitoring
or verificationmonitoring is conducted. In order to be able to assess
the performance, we must have a good definition of when the reme-
diation is a success. In the case of ISCO remediation, chemical
analyses in the soil, the groundwater and the soil are vital, because
• Hasthewishforornecessityofatestremediationbeentakeninto
account?
• Themonitoringplan.Thisprovidestheidealdifferencebetween
the various types of monitoring such as process and performance
monitoring. How is the load removal to be monitored or
determined?
• Arethereenoughconsultationmoments?Whenwilltheprogress
andevaluationreportsbesubmitted?
What do I measure before, during and after ISCO remediation?During each remediation project, there are three measuring
moments:
1. before the remediation, in order to determine the point
of departure.
2. during the remediation, in order to monitor progress, and
3. after the remediation, in order to record the results thereof.
This document will not discuss the monitoring before the
remediation process, the so-called reference monitoring. We will
discuss the progress monitoring conducted during the remediation
and the monitoring conducted after the remediation has been
completed.
Progress monitoringThe monitoring conducted during remediation, also during ISCO
remediation, is known as progress monitoring. For an ISCO remedia-
tion, this progress monitoring comprises three different elements.
• Processmonitoring,totrackandcheckthetechnicalperformance
oftheremediationsystem;
• Riskmonitoring,totrackthehealthandsafetyrisksduring
remediation;
• Performancemonitoring,totrackandchecktheresultachieved.
When a remediation plan is executed, a check must be made in order
to assess whether the technique and the design can be applied at the
location. Processmonitoring is conducted as a quality control
measurement before, during and immediately after injection of an
oxidant. The primary elements of process monitoring are:
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Performance monitoring serves to assess whether an ISCO remedia-
tion actually does what it is supposed to do. A number of performance
monitoring elements can be measured directly in the field:
• thepollutionandanydegradationproductsofthepollution,e.g.
chloride as an indicator for the breakdown during the remedia-
tionofchlorinatedhydrocarbons;
• theoxidant-forpermanganateforinstance,aquick,simple
colourassessmentisavailable;
• auxiliarysubstances,e.g.theiron(II)concentrationandpHin
Fenton’s reagent.
After remediationFirst, the scale of the pollution and the concentrations must be
determined. In the case of ISCO remediation with Fenton’s reagent,
ozone and ozone/peroxide, the final monitoring should be conducted
shortly after the final injection round due to the poor stability of the
oxidant in the soil. In the case of permanganate, the period until
the final sampling can be longer. Following the ISCO remediation,
the soil conditions should ideally return to the initial situation.
Parameters that help us in determining this include: temperature,
the presence of an oxidant residue and redox conditions.
During each in-situ remediation, diffusion from the soil will occur.
As a result of diffusion from the smaller and poorly accessible pores,
the concentration of the pollution in the groundwater slowly increases
again. It is therefore wise to analyse groundwater samples for a long
period of time following the last injection phase. These periods are
three and six months long. In the case of permanganate one is advised
to observe these periods after the purple colour has disappeared from
the cleared up area.
there are three ways in which ISCO contributes to the reduction of
the pollution:
• chemicaloxidation,i.e.breakingdownofthepollution;
• evaporationofthepollution;
• dilutionofthepollutionbyinjectingvarioussolutions.
A groundwater analysis alone will not give you a definite answer
of the contaminant load that has been broken down. Since the soil
organic matter is also broken down, pollution that relates to the
organic matter will be released at the start of the treatment. The
result of this is that - and it has been observed during a host of ISCO
remediation projects - the concentration in the groundwater increases
at the start of the remediation. The concentration then decreases
and will continue to decrease once the contaminant load decreases.
Monitoring during the oxidant injection period is often unnecessary.
As a result of the large quantities of solution to be injected, pollution
in the groundwater may be displaced. To prevent this, oxidants are
to be injected at different injection points alternately, so that the
groundwater is not moved into one direction. Nevertheless, it is wise
to check for diffusion on the edges of the injection area.
52 53
any traces of permanganate, was treated with a purifying agent
containing active carbon. During two injection periods, 2,700 kg
of permanganate were injected as a 4% solution with an output of
1 m3·u-1 and a groundwater extraction of 5 m3·u-1. The verification
monitoring process comprised field measurements for pH, tempera-mpera-
ture, redox conditions, conductivity and permanganate concentra-
tions, plus chemical analyses for PCE and heavy metals. Following
injection, an obvious effect was observed on the redox conditions and
conductivity. Based on the permanganate measurements in the field
plus drillings, it was found that the permanganate stopped having an
effect at 10 m of the injection filters. This could be a result of the soil’s
demand for oxidant. During the active phase of the ISCO remediation,
the PCE concentration in the groundwater fell below the detection
limit. Between the first and second injection phase, the PCE concen-
trations quickly returned to concentrations between 1,000 and 2,000
µg·l-1. Following the second injection phase, diffusion from the soil
was observed, but the groundwater concentrations in the source area
remained between 280 and 360 µg·l-1. In the source area, a load
reduction of more than 90% was observed three months after the
active remediation phase had ended.
The activities of a chemical laundry cause the soil and groundwater
to be polluted with tetrachloroethene (PCE). Due to the relatively low
levels of the groundwater at approx. 4 m -mv, the pollution occurred
in high concentrations, both in the unsaturated and saturated zones
of the soil. The remediation plan therefore intended to tackle the
pollution by means of a ground air extraction system for the unsatu-
rated zone, and groundwater draw-off for the saturated zone. Both
systems were started in 1997. Remediation of the unsaturated soil was
halted in 2000. In 2004, the groundwater draw-off yielded an average
of 200-300 µg·l-1. In the source area, occasional concentrations of
5,000 µg·l-1 were found. The estimated surface area of the residual
pollution amounted to approx. 75 - 100 m2.
It was then decided to apply ISCO. Due to the small amount of
biological activity, the oxygen-rich conditions in the groundwater,
the commissioning party’s wish for a minimum amount of disturbance
and the low NOD value (0.5 - 1.9 g MnO4·kg-1 of soil), it was decided
to tackle the residual pollution with permanganate. The injection
system comprised three injection points and two extraction points.
This configuration made it possible to specifically aim the oxidant
through the residual pollution. The extracted groundwater, including
ISCO remediation with permanganate of residual pollution at a dry cleaner
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ISCO - In-situ chemical oxidation
This document was written on the basis of our own practical experience and a wealth of literature, such as excerpts from conferences, scientific articles, magazine articles, and reports on different ISCO remediation projects. We also consulted various Internet sources, including those of specialist contractors. Below is a selection of the various sources that provide additional information on ISCO.
Conferences are the perfect opportunity to stay up-to-date on the
latest developments in the field of in-situ remediation. Specific
conferences that focus entirely on ISCO, or conferences that have
ISCO remediation as a permanent item on the agenda include:
• thebiennialFZK/TNOconferenceContaminatedSoil,or
ConSoil. Focuses mainly on developments in Europe.
Seealsowww.consoil.de;
• Anotherbiennialconference,thistimeintheUnitedStates:
The International Conference on Remediation of Chlorinated
and Recalcitrant Compounds. This conference often deals with
the latest developments in the field of soil remediation, including
ISCO.Seealsoww.battelle.org/conferences;
• TheannualEuropeanConferenceonOxidationandReduction
Technologies for Ex-Situ Treatment of Water, Air and Soil and
In-Situ treatment of Soil and Groundwater (ECOR) in Göttingen,
Germany. ECOR specialises in ex-situ and in-situ oxidation
and reduction remediation techniques, including ISCO and its
applications. See also www.terratech.com.
There are a number of specialist Dutch magazines that publish the
most significant developments in the field of the environment, such
as: Bodem, Land + Water en Milieumagazine. Other scientific journals,
such as the Technisch Weekblad and Cobouw, often publish interes-
ting articles on in-situ remediation, including ISCO. For the in-situ
remediation company that wants to find out more, we recommend the
Additional information5
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Apart from these sources, there are of course a number of books that
discuss ISCO as a remediation technique. Here is a small selection:
• CGJMPijls,ThJSKeijzer,ECLMarnette,MSumann,FVolkering,
M van Zutphen (2005). In-situ bodemsanering, theorie en praktijk.
Tauw, Deventer;
• RLSiegrist,MAUrynowics,ORWest(2001).Principlesand
practices of in-situ chemical oxidation using permanganate.
BattellePress,MontereyCA,USA;
• ITRC(2005).Technicalandregulatoryguidanceforin-situ
chemical oxidation of contaminated soil and groundwater.
Interstate Technology & Regulatory Council, USA.
following scientific magazines: Environmental Science and
Technology (ES&T), Groundwater Monitoring and Remediation
(GWMR) and Water, Air and Soil Pollution (WASP).
During the past few years, the Internet has become a source of
information for technical developments in the field of in-situ
remediation. Apart from contractors publishing detailed information
on the techniques they offer, the websites of various governmental
institutions (especially those in the USA) are very good sources of
information, where you can also find the very latest details on ISCO.
Here is a small selection:
• www.bodemrichtlijn.nl - the digital version of the Soil
Remediation Techniques Handbook includes a section on ISCO.
SeethechapterLibrary;
• bodem.pagina.nl - the ultimate home page in the field of soil, also
inthefieldofremediationtechniques;
• www.epa.gov-USEnvironmentalProtectionAgency(EPA);
• clu-in.org - Hazardous Waste Clean-up Information
(also from the EPA, but specifically aimed at the technical
element) offers a wide range of documents on ISCO applications
anddevelopments;
• www.frtr.gov - Federal Remediation Technology Roundtable
technology website. Like the clu-in website, it contains lots of
up-to-dateinformation;
• www.itrcweb.org - Interstate Technology and Regulatory Council
website. Contains documents about different techniques and
what is feasible, also from the point of view of the competent
authorities.
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Colophon
TextThomasKeijzer Tauw
Martine van Gool Tauw
Technical Translation
Niels Hartog TNO Built Environment and Subsurface
Reader groupGerrit Boer BSB Zuid
JohnBraam KBBL
Hans Groot Wareco
Hans Niemeijer Province of Gelderland
We extend our thanks to:TwanKanen Mourik Groot-Ammers
Rudi Pelgrum In Situ Technieken
Charles Pijls Tauw
Bert Scheffer Verhoeve Milieu Oost
Roland de Wit Mateboer Milieutechniek
Design VanLintVormgeving,Zierikzee
Printer HoorensPrinting,Kortrijk
Images Tauw (pages 10, 15, 18, 20, 23, 25,
27, 28, 46, 50, 53 and 57)
KBBL(pages15and25)
IST (page 17 and 38)
Verhoeve(page30)
SKB(pages7,46and54)
September 2007